Typically in an automatic transmission mounted in a vehicle or the like, a starting apparatus is interposed between an engine and the automatic transmission to absorb idle rotation of the engine while the vehicle is stopped, and enable power to be transmitted when starting (i.e., when taking off from a standstill). This starting apparatus mainly includes a fluid transmission apparatus (such as a torque converter, a fluid coupling, or the like). Furthermore, fluid transmission apparatuses that have a lock-up clutch that can lock up the automatic transmission with the engine so that the input speed of the automatic transmission is the same as the output speed of the engine are also continuing to become more common. This kind of fluid transmission apparatus requires a supply of circulating oil as a medium for transmitting power and for cooling. Also, engagement pressure needs to be supplied to the lock-up clutch during lock-up. Line pressure is used as the base pressure of the engagement pressure and the pressure of this circulating oil (see Japanese Patent Application Publication No. 2005-240844 (JP-A-2005-240844)).
Incidentally, multi-stage automatic transmissions in particular execute shifts by engaging and releasing clutches and brakes by supplying and discharging hydraulic pressure to and from hydraulic servos of those clutches and brakes in an automatic speed change mechanism, and use line pressure also as the base pressure of the hydraulic pressure used for these shifts. Therefore, if line pressure ends up being supplied to the fluid transmission apparatus when the engine speed is low and the amount of fluid discharged from an oil pump is low, for example, it may take time to obtain the hydraulic pressure required for the shift in the automatic speed change mechanism, and as a result, the shift duration may end up becoming long.
Also, one conceivable way to quickly obtain the hydraulic pressure required for a shift in the automatic speed change mechanism while supplying the required amount of fluid to the fluid transmission apparatus is to increase the size of the oil pump or increase the engine speed. However, in this case, there is the problem that the fuel efficiency of the vehicle ends up being affected by the amount that the size of the oil pump is increased or the amount that the engine speed is increased.